Mostg efficient product&method for removing Green&black growth in the waterline?

[Karlsenkystfiske]

Have taken the mighty "Solringen" on land for maintenance after being left still for 3 months all summer. Overgrown with shells and other biological material I have some work to do in order to get her all clean.
The growth just above the waterline is very stuck. High pressure with turbo nozzle could not lift it. Rotating drill brush and soap/degreaser have removed some, but not all of it. Maybe if I scrub the same spot for a lonfg time... Surely there must be a better way?

 

[Refueler]

Cilit Bang Lime and Rust cleaner was brill for this until they changed the formula ... now its useless.

I now use Spray on Oven Cleaner .... type that foams up and stays working in place ... but needs to be well rinsed off.

Another of course is Oxalic Acid mixed strong and a bit of Wallpaper paste added to create a thin paste to cling where put.

For small areas - I have used Car Wheel Cleaner ....

 

[Baddox]

Soapy water and a brillo pad worked for me. The pad wasn't abrasive enough to damage the boat but still removed the weed residue. A quick polish afterwards brought the shine back.

 

[pandos]

Soapy water, ciff cream cleanser and a green scrubbing pad...

 

[Chiara’s slave]

Soapy water, ciff cream cleanser and a green scrubbing pad...

And a plastic ice scraper for car windows for the really tenacious stuff.

 

[William_H]

I get very similar stain which comes off immediately with oxalic acid in water. I use a spray bottle but keep your nose away or wear a mask. I actually spray the topsides near water line while it is in the water with me swimming alongside. It needs it after 8 weeks in water. By the time I get around the little boat it is clean except for bits missed so I go around again.
Now if oxalic does not move it then try acetone for grease/oil stains. If that fails try bleach. ol'will